Fabrication of an intraocular lens

ABSTRACT

A lens, having an optical power surface, which may have multiple radii portions or aspherical portions as well as spherical portions, is molded in a coined mold. A pair of core pins, positioned within the mold cavity during the lens forming process, will produce a pair of haptic-mounting holes within the lens. As the lenses are subsequently tumbled to remove flash, indentations will form adjacent to the haptic-mounting holes. These indentations allow for tangential attachment of the haptic to the lens which, in turn, enables maximum flexibility without exceeding the width of the optic.

BACKGROUND OF THE INVENTION

The present invention relates generally to the field of intraocularlenses. More specifically, the present invention is related to atechnique for fabricating a mold for making intraocular lenses havingvirtually any surface contour, including non-symmetric surfaces. Theinvention also includes a technique for attaching and securing supportmembers, or haptics, to an intraocular lens, after the lens has beenformed and tested.

Artificial intraocular lenses, used to replace damaged or diseasednatural lenses in the eye, have been widely used in the last twodecades. Typically, such intraocular lenses comprise some type ofoptical element and a support, or haptic, coupled thereto, for properlypositioning and centering the intraocular lens within the eye. Theselenses have typically included hard polymeric or glass optical elementswith metallic or polymeric supports. During the past decade, the medicalprofession has made widespread use of intraocular lenses comprisingpolymethylmethacrylate (PMMA), a hard plastic composition. In general,PMMA lenses are cut on a precision lathe, using diamond cutters orinjection molded, and then carefully post polished by a criticaltumbling process in which the edges of the lenses are radiused andpolished.

Recently, workers in the art have utilized lenses comprising a soft,biocompatible material, such as silicone. Silicone lenses have theadvantage of being lighter in situ than PMMA lenses, and because theyare flexible, they can be folded to reduce their size duringimplantation into the eye in accordance with conventional surgicalprocedures. In the implementation of such a procedure, it is the desireof the ophthalmic surgeon to reduce to a minimum the amount ofastigmatism and trauma induced in the eye. A technique known asphacoemulsification permits the removal of the diseased or damaged lensand the insertion of a new intraocular lens through an incision of aslittle as 3 to 4 millimeters. Unfortunately, this procedure is notcompatible with the insertion of hard PMMA lenses, and surgeons havefound it necessary to increase the length of the incision to at least 8mm to insert such lenses, obviating at least one advantage ofphacoemulsification technology. Methods of producing optical components,such as lenses, have not changed in principle in many years. The mainrequirements are that the optical surface be polished to a highlyaccurate shape. In the fabrication of a soft, biocompatible lens, apolished mold, in the shape required for the correct refraction of lightfor the material selected, is employed. Silicone elastomers, of medicalgrade, have been found ideally suited for this purpose. The uncuredsilicone polymer is introduced into the lens cavity of the mold, in anamount dictated by considerations relating to the lens size, refractivepower, and structure; and allowed to cure, usually by heating the moldto 250° to 350° F. in a press. Several methods of molding the final lenshave been employed and include injection molding, liquid injectionmolding, compression molding and transfer molding.

It is sometimes desirable to have a lens which includes plural regionshaving different spherical radii, an aspherical lens, or a lens havingaspherical portions. A virtue of such lenses is that the various lensportions yield an increase in dioptric power as the radius of curvaturedecreases. A problem with making such lenses is the difficulty inobtaining a satisfactory mold of optical quality, having the desiredchanging radius of curvature. Currently, most molds are made usingoptical grinding or cutting equipment, or electrical discharge machining(EDM). The mold cavity is then post polished using standard opticallapping techniques. The resultant mold yields a lens having squared-offedges, which cannot be dramatically altered to provide a smooth,radiused edge without substantial risk of damaging the lens. Due to thesize of the mold and the difficulties in obtaining an optical finish ona convex surface produced by such a mold, molds for intraocular lenses,having critically measured multiple radii or aspherical portions, usingpresent techniques is very difficult to make and not cost effective.Thus, the present invention offers a method and apparatus for formingmolds having such dissimilar shapes.

In another aspect of the present invention, a method of bonding hapticsto the periphery of an intraocular lens is described. Haptic materialshave included metal loops of various types, however, due tocomplications related to weight and fixation, such structures haveproven undesirable. Presently, polypropylene is a preferred hapticmaterial, although PMMA, nylon, polyimide, polyethylene, polysulfone,and great number of extruded plastics may be used as well. Polypropyleneis very resistant to bonding to silicone. It is imperative that thehaptics not become detached from the optical element after implantation,as this could have severe repercussions.

The current, preferred method for attaching haptics to the opticalelement of an intraocular lens is by way of a mechanical lock. This lockmay be comprised of an anchor, or loop, through and around which thelens material is cured during the molding process of the lens. Oneproblem associated with such a mechanical bonding technique is that themechanical anchor often intrudes into the optical zone of the lens,adversely affecting the visual acuity of the patient. Problems alsoarise when the haptic material is heated to the molding temperature. Ingeneral, excessive heat causes the haptic material to become brittle andcauses degradation of the material. In addition, the angle that thehaptics make with the lens is often critical, ranging from between 0 and10°. If the optical element is formed through and around the haptics, aseparate mold would be required each time it was desired to change theangulation of the haptic. Further, proper angulation of the haptic withrespect to the lens is very difficult to achieve during standard moldingprocesses, as the introduction of the lens material into the mold cavitycan cause the haptics to be slightly offset. In addition, the hapticstend to get smashed as the two halves of the mold are brought togetherand closed. Even if the haptic is properly secured to the lens, and ableto withstand the molding temperatures and pressures, the lens must beoptically tested and approved. A lens rejected for lack of opticalquality would obviate the proper positioning and attachment of thehaptics thereto. It would therefore be preferable to attach the hapticsto the lens after the lens has been formed and optically tested,however, as mentioned above, the bonding of polypropylene to siliconehas proven extremely difficult.

Therefore, there is a need in the art for a technique of makingintraocular lenses having multiple radii portions or aspherical portionsfor providing varying degrees of dioptric power. Further, there is aneed in the art for a method of attaching haptics to intraocular lensesin general, after the lens has been formed and optically tested.

SUMMARY OF THE INVENTION

Briefly, the present invention provides a technique for fabricatingintraocular lenses which may have multiple radii portions or asphericalportions. In a preferred embodiment, such lenses are biconvex lenses andare configured such that the posterior side of the lens is substantiallyspherical, while the anterior side of the lens is comprised of threesections. The superior half of the anterior side of the lens isspherical, having the same radius of curvature as that of the posteriorside. The center of the inferior half of the lens, however, isaspherical, having a precisely defined, steadily decreasing radius ofcurvature. This aspherical section is met by a second spherical section,having a second radius of curvature, larger than that of the superiorhalf. It would be cost-prohibitive to CNC or EDM this configuration toform a mold cavity of optical quality. Accordingly, a reverse mold iscreated, hardened, and pressed into a softer material, leaving animpression in the softer material which defines the aspherical moldcavity.

This technique begins with the creation of a pattern, machined at tentimes the size of the lens on a precision lathe, EDM or CNC machine. Athree-dimensional pantograph machine is then employed to transfer thepattern surface to a workpiece one-tenth the size of the pattern. Thesurface of the workpiece will exhibit a miniature reproduction of thepattern, having the precisely defined surface contours of the pattern onthe face thereof and will be used as a coining mandrel. The coiningmandrel is then hardened and painstakingly polished to produce anoptical surface, while maintaining the surface contours replicated fromthe surface of the pattern. A blank, which will form a mold half, isoptically lapped to produce a flat optical surface. The polished coiningmandrel is then pressed into the blank under tremendous pressure toimpress upon the blank the desired mold cavity configuration. It isimportant that the contacting faces of both the coining mandrel and theblank be polished to optical surfaces, as imperfections in either ofthese pieces will inevitably manifest itself on the resultant lens.

In another aspect of the present invention, a method of tangentiallybonding haptics to the lens is described. In this method, core pins areinset into the mold on diametrically opposed sides prior to theintroduction of the lens material. No mold release agents are necessary,as the lens material does not adhere to the mold surfaces. The lensmaterial forms and cures around the core pins, but does not bond tothem, while the lens is being molded. The core pins are then removed,leaving behind small apertures adjacent the edge of the lens. While thelens is being tumbled and polished, the area of the lens adjacent theseapertures abrades more rapidly than the remaining perimeter of the lens,producing indentations. The indentations enable tangential attachment ofthe haptics to the lens.

Adhesive bonding of the haptics, which are preferably formed ofpolypropylene, PMMA, polyester or other biocompatible materials, tosilicone lenses is accomplished by improving the adhesive properties ofthe polypropylene through surface treatment of the haptic with a highfrequency corona discharge and a silicone primer. The surface-treatedhaptics are then bonded within the apertures adjacent the lens edge witha translucent, nonflowing, soft silicone adhesive. Adhesive bonding ofthe haptic to the lens is preferable in that it permits flexibility inthe angulation of the haptic with respect to the lens. In addition,subsequent attachment of the haptics to the lens obviates the problemsassociated with forming the lens with the haptics intact, such as thetendency of the haptics to become brittle due to the curing temperaturesand the need to machine separate molds for various angular arrangements.Further, subsequent haptic attachment advantageously provides muchflexibility in the choice and use of various haptic materials havingvarying diameters and configurations. Moreover, the optical element maybe optically tested and measured prior to the attachment of the hapticto the lens. In yet another aspect of the invention, a method cfcalculating dioptric power at any point on the varifocal portion of anonspherical lens is discussed.

These, as well as other features of the invention will become apparentfrom the detailed description which follows, considered together withthe appended drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an intraocular lens, made by thetechniques described herein;

FIG. 2 is a perspective view of a reverse mold pattern, ten times thesize of the final reverse mold, having an aspherical portion;

FIG. 3 is an exploded perspective view of the pattern illustrated inFIG. 2, showing the various sections of the pattern;

FIG. 4 is a perspective view of a pantograph, used to replicate thepattern onto the surface of a coining mandrel, one-tenth of the originalsize;

FIG. 5 is a perspective view of a reverse mold, or coining mandrel,having an optical surface polished thereon;

FIG. 6 is an exploded perspective view of a mold forming assembly, usedin the fabrication technique of the present invention;

FIG. 7 is a cross-sectional view of the forming assembly of FIG. 6, justprior to pressing the mold cavity;

FIG. 8 is a perspective view of a mold half formed in the assembly ofFIG. 7;

FIG. 9 is an enlarged cross-sectional view, taken along line 9--9 ofFIG. 8, showing the slight eruption of metal displaced during the moldforming process;

FIG. 10 is an enlarged partial cross-sectional view of the mold half ofFIG. 11, showing the ground-off eruption in phantom lines and anoverflow groove which has been machined around the optical cavity;

FIG. 11 is a perspective view of a top half of a mold made in accordancewith the technique of the present invention;

FIG. 12 is a perspective view of a core pin and post assembly;

FIG. 13 is a perspective view of a bottom half of a mold, showing theinsertion of the core pin and post assembly of FIG. 12 in dashed lines;

FIG. 14 is a perspective view of the mold halves situated one over theother prior to the formation of a lens;

FIG. 15 is a perspective view of a newly molded lens, showing theflashing, sporadically disposed about the periphery of the lens;

FIG. 16 is a cross-sectional view, taken along line 16--16 of FIG. 15;

FIG. 17 is a perspective view of an edge of the lens adjacent theaperture formed by the core pin subsequent to the tumbling of the lens;

FIG. 18 is a partially exploded perspective view of a forming mandrelused for making a control haptic;

FIG. 19 is a top plan view of the forming mandrel illustrated in FIG.18;

FIG. 20 is top plan view of the forming mandrel illustrated in FIGS. 18and 19, showing the control haptic being formed;

FIG. 21 is a plan view of a control haptic;

FIG. 22 is a partial cross-sectional view of an edge of a lens,illustrating the aperture being filled with adhesive;

FIG. 23 is a partial cross-sectional view of an edge of a lens, showingthe tangential bonding of a haptic into the hole;

FIG. 24 is a cross-sectional view, taken along line 24--24 of FIG. 23,showing the angulation of the haptic within the hole;

FIG. 25 is a perspective view of a dihedral holding fixture used tomaintain the haptics at a predetermined angle within the lens while theadhesive cures;

FIG. 26 is a cross-sectional view, taken along line 26--26 of FIG. 25,showing the disposition of a lens within the dihedral holding fixture;

FIG. 27 is a graph plotting the radius of curvature of the asphericalportion of the lens;

FIG. 28 is a partial cross-sectional view of an alternative coiningassembly; and

FIG. 29 is a profile of an intraocular lens, schematically illustratingthe dioptric power increase of light passing through various portions ofthe lens, having various radii of curvature.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to the drawings in detail, wherein like reference numeralsdesignate like elements throughout the several views thereof, there isshown generally at 10 in FIG. 1, an intraocular lens formed using thetechniques of the present invention. Preferably, the intraocular lens 10is a biconvex lens having a first, or anterior side 12 and a second, orposterior side (not shown). The posterior side will reside in thecapsule of the eye adjacent the vitreous humor, and is substantiallyspherical. The anterior side 12, however, as schematically illustrated,is asymmetric, and is formed of three sections 14, 16, 18. The upper, orsuperior section 14 occupies the upper half of the lens and issubstantially spherical, having essentially the same radius curvature asthat of the posterior side of the lens. The center section 16 adjacentthe superior section 14, extends from the center of the lens to thelower quarter, and exhibits an aspherical surface, having a graduallydecreasing radius of curvature. The third section 18 of the lens 10 isalso spherical, but exhibits a longer radius of curvature than that ofthe superior section 14 so as to provide a flatter surface and thusgreater strength and thickness near the edge 20 of the lens, at thejuncture of the two spherical sections 14, 18. A pair of supportmembers, or haptics 22, 24 are secured to the lens 10 on diametricallyopposed sides, and aid in centering the lens 10 within the eye afterimplantation. The superior, or control haptic 22 is provided with ahorseshoe-like, or eyelet shaped, kink 26 which enables the ophthalmicsurgeon to readily determine which is the superior portion 14 of thelens 10 and permits manipulation of the lens 10 during surgery.

A pattern 28, or reverse mold of the desired surface of the anteriorside 12 of the lens 10, preferably made out of aluminum with a CNCmachine and scaled ten times larger than the desired size, isillustrated in FIGS. 2 and 3. As most clearly illustrated in FIG. 3, thepattern 28 comprises three major components: a large semi-circular block30, a small semi-circular block 32, and an arcuate block 34, having anouter diameter corresponding to the diameter of the large semi-circularblock 30, and an inner diameter corresponding to the diameter of thesmall semi-circular block 32. The blocks 30, 32, 34, are securedtogether by a plurality of bolts 36. The larger semi-circular block 30has a spherical surface 38, and corresponds to that portion which willultimately be the superior half 14 of the anterior side 12 of the lens10. Likewise, the arcuate block 34 corresponds to the outer, inferiorsection 18 of the lens 10, and is also provided with a spherical surface40, although somewhat flatter than that of the large semi-circularblock.

It is noteworthy that when making the pattern, the radius of curvatureof the various portions must be shorter than that of the desired surfaceof the mold cavity to allow for "spring back" of the coined surface.Specifically, it has been found that the center of the mold cavity,which is deeper than the periphery, "springs back" more than theperiphery, since it has yielded more than the periphery. Empirical datahas shown that for a stainless steel mold cavity, the coined mold willhave a radius of curvature which is 1 to 2% larger than the radius ofcurvature of the coining mandrel. A correction factor for thisdifference is made in the pattern by reducing its radii of curvature by1 to 2%. In addition, silicone lenses made in such a mold tend to shrinka uniform 3.7% during the lens forming process. Therefore, the pattern,in addition to having shorter radii of curvature, should be enlarged bya factor of 3.7% to allow for such shrinkage.

The radius of curvature of an optical element is proportional to thefocal length of that element. As the radius of curvature of an opticalelement decreases, the dioptric power, which is defined as the inverseof the focal length when measured in meters, increases. The smallsemi-circular block 32 is configured such that the radius of curvature,on the surface 42 thereof, steadily decreases from a first value, R₀,equal to the radius of curvature of the large semi-circular block 30, toa lower value, R_(N), determined by the desired change in the base powerof the varifocal, or aspherical portion 16 of the lens 10.

In a biconvex lens, as shown in FIG. 1, and schematically illustrated inFIG. 29, the entire posterior side 200 and the superior half 14 of theanterior side 12 of the lens are of fixed curvatures which determine thebase power of the lens after implantation in the eye. The inferior halfof the anterior side 12, is capable of providing varying levels ofaccommodation by virtue of the aspherical portion 16 of the lens. Asnoted above, the dioptric power of an intraocular lens is typicallycontrolled by varying the anterior and/or posterior radii of the opticalelement. If, for example, as illustrated in FIG. 29, the posterior side200 is of a fixed radius of curvature, corresponding to a dioptric powerof 9 diopters, and the superior half 14 of the anterior side 12 exhibitsthe same radius, and thus the same power of 9 diopters, then lightimpinging on the lens in this area, as designated by line 202, would befocused with a dioptric power of 18 (9+9) diopters. As the centersection 16 of the anterior side 12 under goes a change in its radius ofcurvature, the focal point of light impinging therethrough would alsochange. If, for example, the intraocular lens were designed provide asteadily increasing power of 6 diopters, light impinging on the lens 1/6of the way down the aspherical section, as designated by line 204, wouldbe focused with a power of 19 diopters (9+9+1), whereas light impingingon the lens at the bottom of the aspherical portion (line 206) would befocused with a power of 24 diopters (9+9+6). Finally, light impinging onthe inferior portion of the lens, corresponding to the flatter sphericalsection of the lens 18, and designated by line 208, would have a powerof 16 diopters (9+7). This effect was demonstrated in theory by Lee T.Nordan in U.S. Pat. No. 4,769,033, entitled "Intraocular MultifocalLens," issued on Sept. 6, 1988, a continuation-in-part of U.S. Patentapplication Ser. No. 069,197, filed on July 2, 1987, now abandoned.

FIG. 27 schematically illustrates the changing radius of curvature (R₀ .. . R_(N)) throughout the varifocal portion of the lens. The radius ofcurvature (R₀) begins at the same radius as that of the sphericalportion, and then gradually decreases. The radius of curvature (R_(x))of the varifocal or aspherical portion of the lens, can be determined atany point by the equation: ##EQU1## and where: ΔP=the total change inpower from R₀ to R_(N;)

V=the width of the varifocal portion of the lens;

N₂ =the index of refraction of the lens; and

N₁ =the index of refraction of aqueous in situ.

Thus, the aspherical portion of the lens is a solid of rotation, formedby rotating the curve generated by the above equations, about a linewhich passes through the initial radius R₀, to form the surface.

The power increase, or "add" Px at any point may be defined by theequation:

    P.sub.x =P.sub.0 +(X*ΔP)/V

where:

P₀ =the power at R₀ ; and

X=the distance from P₀ to P_(x).

As the radius of curvature of the varifocal portion of the lensdecreases, the center of curvature for each radii shifts. The locus ofthe center of curvature of the changing radii follows an arcuate path,and is approximated by the equation:

    S.sub.x ≈V(1-R.sub.x /R.sub.0).

A pantograph 44, which is an apparatus for transferringthree-dimensional tracer pin motions to a cutting tool is illustrated inFIG. 4. The cutting tool 46 moves in the same direction as the tracerpin 48, at a preset, duplicating ratio. The pantograph 44 is employed toreplicate the contours of the pattern 28 onto a workpiece 50 which is,in the preferred embodiment, ten times smaller than that of the patternitself. The pattern 28 and the workpiece 50 are clamped in conjugatepositions at roughly the same level to ensure alignment of the cutter 46and the tracer pin 48. Preferably, the cutter 46 is a high gradetungsten carbide tool, and spins at approximately 20,000 rpm. If thediameters of the tracer pin 48 and the cutter 46 are selected inaccordance with the duplicating ratio, and if the points of the tracerpin and cutter are in alignment with the axis of the horizontal pivotshaft (not shown), the cutter 46 will replicate all of the patterncontours onto the workpiece 50 at the designated ratio. The patternsurface is replicated by carefully drawing the tracer pin 48 across thesurface of the pattern 50 in small, circular strokes in steps ofapproximately 0.010". It is noteworthy that reproduction of the pattern50 at one-tenth the desired size is advantageous in that any slighterrors on the surface of the pattern will be proportionally reduced tothe scale reduction out on the replica 54, to acceptable tolerances. Thetracer pin 48 may be driven manually or by a CNC machine (not shown).

The replica 54 is to be used as a coining mandrel for coining opticalsurfaces. It is to be understood that the term coining is used to definethe permanent deformation of a soft material, as impressed by a hardermaterial. Preferably, the replica, or coining mandrel 54, is a small,cylindrical piece of high-grade, hardenable alloy tool steel, capable ofreaching a hardness of 58 Rockwell, Scale C (R_(c)). Most preferably,D-2 steel is used. Once the coining mandrel 54 has been etched with ascaled-down reproduction of the pattern 50, the rough edges developedduring the replication process are polished off. Significantly, theperipheral edge 55 of the coining mandrel 54 (FIGS. 5 and 7) is radiusedsuch that when an optical mold is coined, the convexity of the resultantmold cavity will yield a smoothly radiused product. Thus, when twocoined mold halves are brought together to form a biconvex lens, theresultant lens will exhibit an ogive shape with a blended, radiusededge, eliminating squared corners typical of traditionally moldedintraocular lenses. Further, lenses made in a coined mold cavity willexhibit only one flash line which can be easily abraded away usingstandard tumbling techniques, whereas the squared corners of atraditionally molded lens cannot be tumbled to produce an ogive shapedintraocular lens.

The coining mandrel 54 is then heat treated in an oven to harden the D-2steel throughout to a hardness of between 58 to 62 Rockwell, Scale C(R_(c)), and most preferably, 60 R_(c) which corresponds to a tensilestrength of 320,000 p.s.i. Because oxygen tends to leave an undesirablecoating on the surface of the steel during the heat treating processwhich would have to be sand-blasted off, the coining mandrel 54 ispreferably hardened in one of two ways. The preferred way is to evacuatethe air out of the oven to produce a vacuum environment and heat thecoining mandrel by radiation to approximately 1300°. The coining mandrelis then allowed to slowly cool and will emerge from the oven within thedesired range of hardness. As the steel is heated and cooled, its grainstructure changes in a predictable manner. Another way of heat treatingthe coining mandrel to a hardness of between 58 and 62 R_(c) is to heatit in a Nitrogen oven. This process is much slower than the vacuummethod, as the coining mandrel is heated primarily by convection ratherthan by radiation.

During the heat treating process, the hardness, strength and wearresistance of the coining mandrel are increased, however nicks,scratches and impurities in the steel are also magnified. Thus, once thecoining mandrel 54 has been heat treated and hardened to 60 R_(c), thereverse mold surface 56 must be polished to an optical surface. Thegeneral practice is to polish the surface 56 of the mandrel 54 with asuccession of polishing agents, progressing from a coarse grit to afiner grit. Because of the nature and intended use of the coiningmandrel, as well as the minute surface area of the reverse mold surface,the coining mandrel must be hand polished under a microscope, allowing abetter polish.

Polishing the surface 56 of the coining mandrel 54 is a very tediousprocess, and requires hours of meticulous work. The first step in theoptical polishing of the coining mandrel is to remove all of the crownsand crests from the surface which were magnified during the hardeningprocess. This is accomplished by applying a small amount of fine machineoil and 600 grit silicone carbide material to the surface of the coiningmandrel and polishing it with small, circular motions using the end of abrass rod followed by the use of 1,000 grit silicone carbide. To ensurethat the surface of the coining mandrel is not being over polished andthat the precisely calculated radii of curvature are maintained, acomparator is used during each step. Once the crowns and crests havebeen polished off the surface of the coining mandrel, machine oil andaluminum oxide (Al₂ O₃), having a grit size of one micron (1 μ), isemployed as a polishing agent, and the surface 56 of the coining mandrel54 is further hand polished with wood sticks in small circular motions.Next, using a dremmel, or a hand held drill, having a hardened feltsurface, the coining mandrel is optically lapped using 0.3 μ Al₂ O₃ andfine machine oil. Finally, the coining mandrel is tumbled in a standardtumbler, as commonly used in the field to tumble and polish intraocularlenses. The tumbler is filled with 1 and 2 mm glass beads, fine machineoil of the type used during the above polishing steps, an antisettlingagent and mineral spirits. Preferably, the antisettling agent is fumedsilicone dioxide, having a particle size of between 0.7 to 2.7 angstroms(Å), as made commercially available under the name Cab-0-Sil fumedsilica. The fumed silica is used as a suspending or antisettling agentin the tumbler and accelerates the polishing process during tumbling. Inaddition, it is noteworthy that tumbling media such as water or alcoholare not suitable for use in the tumbler when polishing the coiningmandrel 54 as these agents would cause electrolysis, which, in turn,would etch the surface 56 of the coining mandrel. Upon cessation of thetumbling process, the coining mandrel should emerge having a highlypolished optical surface of the desired configuration.

FIG. 5 illustrates a hardened, polished coining mandrel 54 which is tobe used to stamp its impression into a blank of a softer material,preferably having an optical finish on the face thereof, so as to forman optical power surface within a concave mold cavity. An optical powersurface is one which is contoured to focus light rays so that theyconverge or diverge to form an image. As the coining mandrel has beenhardened to 60 R_(c), the choice of softer materials would appearendless. As illustrated in the partial cross-sectional assembly of FIG.28, for example, the coining mandrel 54 could be pressed into a polishedpiece of sheet metal 57, having a resilient backing 59, such as dierubber, placed thereunder. When coining a mold cavity into such a softmaterial, the coining mandrel 54 need not be hardened to 60 R_(c), butcan be as soft as 40 R_(c). As the mandrel 54 is pressed into the sheetmetal 57, the sheet metal permanently deforms to assume a reverseconfiguration of the surface 56 of the coining mandrel 54. The rubberbacking 59 will yield to the deformation of the sheet metal 57 duringthe coining process, however will spring back after the coining iscompleted and the assembly disassembled. It is noteworthy that a minimalamount of pressure is required to create a mold cavity in the sheetmetal 57 due to the resilient nature of the rubber backing 59, and thethinness of the sheet metal 57 itself. Molds formed in this manner havethe advantage of being light and inexpensive, however, the longevity andnumber of uses of such a mold is severely limited. Accordingly, in theinterest of making a long lasting mold, any grade of good qualitystainless steel should be used. Preferably, the blank 58 (shown in FIGS.6 and 7) is formed of either a 300 type series or a 400 type seriesstainless steel. Presently, the 300 series is preferred, with 203 or 303stainless steel proving well suited.

The blank 58 is machined in the desired shape and thickness, and theface 60 is optically lapped in a manner as is well known in the art.Preferably, the face 60 of the blank is polished in a series of steps,beginning with 320 grit sandpaper and oil, and proceeding to finergrades of sandpaper, having grit sizes of 400 and 600. The blank is thenpolished using a lapping plate, having a urethane cover using 1 μ Al₂ O₃and water. Finally, the face 60 of the blank 58 is optically finishedwith a rotary polisher, having a urethane felt cover, in a 0.3 μ Al₂ O₃and water slurry.

Following the optical polishing of the face of the blank, a mold cavityis ready to be formed. As shown in FIGS. 6 and 7, a pair of drillbushings 62, 64, are utilized to maintain the relative positioning ofthe coining mandrel 54 with respect to the diametric center of thepolished blank 58. Preferably, the bushings are formed of tool steel, asthey will ultimately be subjected to exceptionally high loads. The outerbushing 62 is cored and has an inner diameter 66 sized to receive andcenter the polished blank 58 with minimal clearance about the peripherythereof, so as to ensure that the blank will not move during the moldformation process. Similarly, the inner bushing 64 is also cored, havingan outer diameter 68 selected such that the inner bushing 64 will becentered with respect to the outer bushing 62 and an inner diameter 70,for centering the coining mandrel 54 will be centered with respect tothe blank 58. The inner bushing 64 is further equipped with a flange 72,adapted to rest on the upper rim 74 of the outer bushing 62 to maintaina small gap 76 between the bottom surface 78 of the inner bushing 64 andthe blank 58.

To form a mold cavity, the outer bushing 62 is placed on a hardenedsurface 80. The blank 58 is inserted into the core 66 of the outer drillbushing 62, with the polished side up. It is important to execute carein the insertion of the blank 58 into the bushing 62, as scratches onthe surface 60 of the blank 58 may result in a mold cavity which yieldsflawed lenses. The inner bushing 64 is then inserted into the core 66 ofthe outer bushing 62, so that the flange 72 rests on the upper rim 74 ofthe outer drill bushing 62 and finally, the coining mandrel 54 islowered into the core 70 of the inner bushing 64 until it just touchesthe surface 60 of the blank 58. A second hardened surface 82 iscarefully set on top of the coining mandrel 54, and the formationassembly 84 is put into a hydraulic press (not shown).

It is noteworthy that the coining mandrel 54 should extend outwardlyabove the flange 72 of the inner bushing 64, by an amount equal to thedesired final depth of the mold cavity, taking into account the amountof compression, or shrinkage of the coining mandrel expected during thepressing of the mold cavity. Preferably, the coining mandrel 54 extends0.043 inches above the flanged surface 72, allowing 0.012 inches forcompression of the coining mandrel under full load, and will yield animprint having a final depth of 0.031 inches. Because the 0.043 inch gap88 is directly related to the desired depth of the resultant moldcavity, the hydraulic press may be slowly and steadily loaded until thegap 88 disappears. In general, it takes a load of between 7 and 10 tonsto stamp the coining mandrel impression into the steel blank at thedesired depth. Preferably, the hydraulic press is loaded to 10 tons toensure proper deformation of the mold cavity. A load of this magnitudeimposes a pressure in excess of 400,000 p.s.i. upon the surface 56 ofthe coining mandrel 54. In order to allow for the creeping of thematerials, the press remains under full load for approximately 15minutes after the gap 88 disappears

As mentioned above, upon application of full load, the coining mandrel54 compresses 0.012 inches. In addition, a radial expansion ofapproximately 0.001 inches in diameter is also experienced. However, thecoining mandrel is not deformed beyond the elastic limit of thematerial, and therefore returns to its original form upon removal of theload. Unlike the coining mandrel 54, the stainless steel blank 58 has amuch lower yield strength and therefore undergoes permanent deformationupon application of the load. Thus, not only does the newly formed moldhalf 90 exhibit a mold cavity 92, having a reverse imprint of thesurface 56 of the coining mandrel 54 at the desired depth, as shown inFIG. 8, but also undergoes a radial expansion, resulting in aninterference fit within the core 66 of the outer bushing 62 as well as aslight eruption 94 (FIG. 9) about the periphery of the mold cavity 92.After the load has been removed, the coining mandrel 54 and the innerbushing 64 are lifted from the formation assembly 84. The pressed moldhalf 90, however, must be forced out of the outer bushing 62 due to theinterference fit caused by the radial expansion of the mold half 90.Significantly, during the mold forming process, slight imperfectionspresent on the surface 60 of the blank 58 in the localized area of themold cavity 92 are ironed out. Further, due to the tremendous forceapplied to the materials, the porosity in the mold cavity 92 issubstantially decreased, resulting in a smoother, higher quality opticalsurface than was present on the original optically polished blank, andthe deformation of the blank material work hardens, resulting in aharder, more durable surface.

As shown in FIG. 14, the mold 96 used to form the biconvex intraocularlens 10 of the present invention comprises an upper mold half 98 with anupper concave cavity 100 and a lower mold half 90 with a lower concavecavity 92. Thus, in order to complete the mold 96 for a biconvex lens10, a second, or upper mold half 98 must be made. Preferably, the moldcavity 100 of the upper mold half 98 will have a spherical surface whichwill provide the desired additional base power of the lens. The uppermold half 98 is made in the same manner as the lower mold half 90 withthe exception of the surface configuration of the mold cavity. The uppermold cavity 100 is preferably spherical, having a radius of curvatureselected in accordance with the desired refractive power of theresultant lens. Having formed the concave cavities 92, 100 in each ofthe mold halves 90, 98, the eruptions 94 (FIG. 9) surrounding theperiphery of each cavity must be ground off. Advantageously, each moldcavity 92, 100 was pressed in to a depth of 0.031 inches to allow forimperfections in the blank 58, as well as these eruptions 94. To protectthe optical surface of the mold cavities 92, 100 during subsequentprocessing, an adhesive backed disc 193, or other type of covering,having a light adhesive backing to prevent slippage and having a knownthickness, is carefully placed on the surface of each mold cavity duringthe grinding and machining processes. As shown in FIG. 10, the face 102of each mold half 90, 98 is ground down until a final mold cavity depthof 0.025 inches is attained.

With the adhesive backed disc 193 still in place, an overflow groove 104is machined using a lathe, around the periphery of each mold cavity 92,100. A thin ridge 106, referred to as the mold shut off, or flash line,is created intermediate the groove 104 and the respective mold cavity92, 100 so that concentric circles are formed about the mold cavity. Theflash line 106 defines the outer limits of the molded lens. Asillustrated in FIG. 13, in order to ensure proper alignment of the moldhalves 90, 98 during the molding process, a pair of alignment dowel pins108, 110, are secured to the bottom half of the mold 90 in aconventional manner. Associated mating holes 112, 114 are drilled intothe top half of the mold 98 (FIG. 11) to receive and retain the dowelpins 108, 110 during the molding process. Each mold half 90, 98 ismachined to provide a pair of elongate grooves 116, 118 on diametricallyopposed sides of the mold. The elongate grooves 116, 118 aresemi-cylindrical in cross-section and are adapted to receive andmaintain the positioning of a pair of core pins 120, about which thesilicone lens material will cure during its production. To furtherensure the stability of the core pins within the mold cavity during theproduction of the lens, a pair of small dowel pins 122, 124 is providedin the overflow groove 104, on opposite sides of each core pin 120, tosandwich the core pin therebetween. Advantageously, as illustrated inFIGS. 12 and 13, each core pin 120 is secured to a post 126, which isremovable from the bottom mold half 90. Thus, after the lens is formed,the core pins 120 may be lifted from the mold, together with the lens sothat the core pins do not tear the lens during the removal of the lensfrom the mold. In actual practice, the lens is removed from the mold bypushing the posts 126 upwardly from the bottom half of the mold 90through the hole 127 with a lifter pin (not shown). In this manner, theoptical power surfaces of the mold are less likely to be damaged byremoving tools being inserted under the lens.

FIG. 14 illustrates a complete mold assembly 96. The upper and lowerhalves of the mold 90, 98 are relatively movable towards and away fromeach other to allow the introduction of material which will form theoptical element therein. Preferably, the lenses are produced viacompression molding, although other molding processes, such as injectionmolding, may also be employed. Silicone, in a liquid form, having avolume somewhat greater than that of the two mold cavities is introducedinto the lower mold cavity 99. Preferably, about 0.025 milliliters ofuncured, liquid silicone polymer is used to form the lens. The upperhalf of the mold 98 is then brought into engagement with the lower half92 so that the alignment dowel pins 108, 110 are met by the associatedmating holes 112, 114. Once the mold 96 is closed, the excess volume ofsilicone will leak out between the mold parts and into the overflowgrooves 104. The mold 96 is then heated for a predetermined time at anelevated predetermined temperature that will polymerize the monomerslocated therein into a solid polymer. In the preferred embodiment, themold is heated for 10 minutes at 300° F. Following the polymerization ofthe optical element material, the mold is opened, and the opticalelement is removed therefrom.

As mentioned above, the core pins 120 are lifted from the mold alongwith the optical element. The core pins are then carefully removed byslowly twisting and then withdrawing the them in a plane parallel to thelens. As illustrated in FIGS. 15 and 16, the resultant lens 128 includesa pair of diametrically opposed apertures 130, 132 corresponding to thearea from which the core pins 120 were removed. In addition, a smallamount of flash 134, created during the production of the lens at theflash line 106 will be sporadically disposed about the edge 136 of thelens 128. Significantly, there is only one flash line 106 on thejust-formed lens 128, and the edge 136 is ogive in shape. The lens 128is then tumbled to remove the flash 134 from the periphery of the lensand to polish the edges thereof.

Preferably, the tumbler is filled with 1 to 6 mm glass beads, isopropylalcohol, and fumed silicone dioxide. Typically, Al₂ O₃ is used as thepolishing agent when tumbling PMMA lenses to speed up the tumblingprocess and water is used as the tumbling medium. Undesirably, however,Al₂ O₃ tends to leave a residue on silicone lenses and therefore, fumedsilicone dioxide is used as the polishing agent to accelerate thetumbling process. When using fumed silicone dioxide as a polishing agentand water, the silicone lenses tend to float out and not polish.Isopropyl alcohol, however, has a lower surface tension than water, anda lower specific gravity than silicone and will allow the lenses tosink, thereby making it an ideal tumbling matrix. The isopropyl alcoholhas another advantage in that the silicone lens material absorbs aportion of the alcohol, causing the lenses to uniformly swell an averageof 7%, which in turn, lowers the tear strength of the lens material. Asthe tear strength decreases, the abrading process, caused by thetumbling action of the tumbler, is further accelerated.

The tumbling process tends to abrade more rapidly at lip or margin 138of the holes 130, 132 formed by the core pins during the production ofthe lens because this area of the lens is thinner. This is significantin that, as illustrated in FIG. 17, at the cessation of the tumblingprocess, the optical element 140 is left with an indentation 142proximate the holes 130, 132. Further, the flash, created during theproduction of the lens in the area where the two mold halves met,substantially disappears after tumbling, leaving a smoothly radiused,ogive shaped lens having a blended, radiused edge. In addition, a thinlayer of fumed silicone dioxide will be present on both the outersurface of the lens, as well as the surface within the holes 130, 132.It has been found that this residue improves subsequent adhesive bondingof the haptics 22, 24 within the holes 130, 132 and is therefore left onthe inner surface thereof. The fumed silicone dioxide residue on theouter surface of the lens, however, will be rinsed off, using standardcleaning and extraction techniques.

FIGS. 18-20 illustrate a forming mandrel 144 for making control haptics22. Haptics 22, 24 may be formed from any material, but are preferablyformed from a solid polymer member, designed to be relatively thin andflexible, yet provide sufficient support for the optical element 140.Materials found well suited to the formation of haptics includepolypropylene, PMMA, polyimide, polyethylene, nylon, and great number ofextruded plastics. Preferably, the haptics are formed of polypropylene,or any 5-0 medical non-abradable suture, having a substantially circularcross-section of approximately 0.006 inches in diameter, as commonlyavailable from Ethicon, a division of Johnson and Johnson, as well asDavis and Geck, a division of American Cyanamide. The forming mandrel144 comprises a base 146 upon which a pair of forming blocks 148, 150are mounted. Block 148 is adapted to form the distal, or free end 152 ofthe haptic while block 150 is precisely formed to the desired contoursof the proximal end 154 of the haptic. The blocks 148, 150 arepositioned on the base 146, adjacent one another, leaving a small void156 therebetween.

A control loop pin 158, sized slightly larger than the void 156, isprovided for the formation of the horseshoe-like kink 26, characteristicof the control haptic 22. The control loop pin 158 is sized such thatwhen the suture material is wrapped around it, as illustrated in FIGS.18-20, the combination of the control loop pin 158 and the suturematerial is larger than the void 156. This is significant in that itwill yield a control haptic 22, having a control loop 26 with a kinkedportion which is greater than 180°, but less than 360°, to assist theophthalmic surgeon in more readily determining which is the superiorside of the lens. More simply stated, the kinked portion of the controlloop 26 is at least semi-circular, having an eyelet-like shape, but doesnot form a complete circle. As illustrated more clearly in FIGS. 19 and20, the control loop pin 158 is placed between the blocks 148, 150 andboth ends of the suture are passed through the void 156. The suture 160is then pulled tightly against the blocks 148, 150, conforming to thecontours of the forming mandrel 144, and secured thereto, preferably bytying a knot in the suture material, intermediate blocks 148, 150 andopposite the control loop pin 158. A retaining bar (not shown) is placedagainst the control loop pin 158 intermediate the blocks 148, 150 tobias the suture material 160 toward the pin during the remainder of thecontrol haptic forming process. The wrapped forming mandrel is thenplaced in a Nitrogen oven and heated at a temperature of between 300° F.and 350° F. for approximately one hour. Preferably, the suture materialis heat set at 320° F., during which time it will deform to assume theshape of the forming mandrel 144, and produce a control haptic 22. Afterthe mandrel and haptics have been allowed to cool, they are cut off ofthe forming mandrel with a razor blade along grooves 162 and 164.Haptics without the control loop may also be formed by the sameprocedure, without the use of the control loop pin. The haptics are thentumbled in a standard intraocular lens tumbler, using the standardproportions of water, 0.3 μ Al₂ O₃ and glass beads to round off the endsof the haptics. The resultant control haptic 22 is illustrated in FIG.21. The proximal end 154 of the haptic is somewhat bent at an angle, sothat the haptic, when bonded to the optical element 140, will betangential thereto. Prior to bonding the haptics 22, 24 within theapertures 130, 132 formed in the lens, they must be surgically cleaned.This is accomplished by thoroughly rinsing the haptics in isopropylalcohol, heated to about 150° F.

In order to improve the adhesive properties of the polypropylene suturematerial from which the haptics are made, a high frequency coronasurface treater (not shown) is used to surface charge the proximal end154 of the haptic. Such surface treatment is not permanent, and decayswith time to some limiting value which is dependent upon the particularmaterial being used. Further, corona treated surfaces are notmechanically durable, and should therefore be disturbed as little aspossible. The proximal end of the haptic, which is to be surface treatedby the corona discharge is passed beneath an emitting electrode at aspeed and distance from the electrode which is determined by the amountof treatment required.

Because of the sensitivity of the surface treatment, the treated end ofthe haptic is preferably coated with a primer immediately after beingpassed through the corona discharge. Preferably, a specially formulated,one component unpigmented silicone primer, as available from McGhanNuSil Corporation, and sold under the name CF1-135 High TechnologySilicone Primer, is used. This primer is an air-drying primer, designedto improve the adhesion of cured silicones to various substrates. Auniform thin coat of primer should be applied to the proximal end of thehaptic following treatment of the surface. This may be accomplished bybrushing, wiping, dipping or spraying the primer onto the haptic,although dipping is the preferred method. The primer is then allowed tohydrolyze, or air-dry on the surface of the haptic, at least two hoursprior to bonding. While the adhesion of the primer to the haptic is muchimproved after the haptic has been subjected to the corona discharge, itis sometimes necessary to dip the proximal end of the haptic in theprimer several times before it is uniformly coated. To further improvethe adhesion of the haptics 22, 24, within the holes 130, 132, theproximal end of the haptics may be dusted with fumed silicone dioxideafter the primer has been allowed to dry.

Following the preparation of the haptics 22, 24 for bonding to theoptical element 140, a silicone adhesive 166 is drawn into a 1 cctuberculin syringe 168, shown in FIG. 22. Preferably, the adhesive isRTV-118 silicone rubber adhesive sealant, as commonly available from theSilicone Products Division of General Electric. Alternatively, theadhesive can be medical adhesive silicone type A, as manufactured by DowCorning Corporation, under the name Silastic. These adhesives are easilyapplied, translucent, non-flowing soft silicone adhesives, ideallysuited for bonding silicone elastomers to itself as well as othersynthetics. A 30 gauge needle 170, having a diameter of 0.012", and ablunt end 172 which has been cut off and polished round, as illustratedin FIG. 22, is secured to the end of the syringe 168. Prior to theinjection of the adhesive 166 into the apertures 130, 132, the needle170 is fully inserted into the aperture. The adhesive 166 is then slowlyinjected and the syringe slowly withdrawn from the aperture until theaperture is approximately two-thirds full of adhesive. It is importantthat the syringe needle 170 be fully inserted into the aperture andbacked out of the aperture while the adhesive is being injected, as airpressure in the aperture would tend to force the adhesive outward. Theproximal end 154 of the haptic is then inserted into the adhesive-filledaperture as illustrated in FIG. 23, displacing a small quantity of theadhesive as illustrated in FIG. 24.

It is beneficial to have as long a haptic as possible without undulyincreasing the size of the intraocular lens. Longer haptics have theadvantage over shorter haptics in that they are less rigid,substantially softer and more flexible and, most importantly, lesstraumatic to the eye after implantation. A haptic that completelyencircles the optical element of the intraocular lens, however, wouldnot be preferable, as it would increase the surface area of the lens,necessitating a larger incision into the eye for implanting.Fortunately, because of the indentation 142 at the lip 138 of the lens140 formed during the tumbling process, and the angle at which theproximal end 154 of the haptic is subtended, the haptic emergestangentially from the lens. The tangential alignment and bonding of thehaptic with the lens enables the implementation of a haptic having themaximum possible length without necessitating an increase in width. Thisis significant in that it allows one to use a longer haptic, having theaforementioned advantages of suppleness and flexibility which areinstrumental in providing a comfortable and non-irritating means forfixating and properly positioning the intraocular lens within the eye.In addition, since the width of the intraocular lens is not affected bythe increased length of the haptic, the advantage of smaller incisions,made possible by the advances in phacoemulsification technology andassociated with soft, foldable intraocular lenses is preserved.Advantageously, as shown in FIG. 24, because the haptic is one half thediameter of the aperture, it may be disposed at any number of desirableangles with respect to the lens.

FIGS. 25 and 26 illustrate a dihedral fixture 174, having a pair ofupwardly sloping sides 176, 178 and a pair of opposing sidewalls 180,182 disposed along the upper edges 184, 186 of the sloping sides.Preferably, the dihedral fixture 174 has an included angle of 172° so asto provide for a 4° inclined surface on each of the sloping sides 176,178. Centrally disposed between the opposing sidewalls 180, 182 of thefixture are a plurality of depressed receptacles 188, resting in avalley 190 created by the sloping sides 176, 177 of the forming fixture174. Each receptacle 188 is sized to accommodate one intraocular lens.Small coves 192 are cut into the opposing sidewalls 180, 182 to providereceptacles for the haptics 22, 24 during the time the adhesive 166 iscuring. The intraocular lens 10 is carefully placed into the depressedreceptacle 188 which, because of its sunken disposition, adds an extradegree to the angulation of the haptic with respect to the lens,resulting in an intraocular lens 10 having haptics 22, 24 set at a 5°angle with respect to the lens.

As a final production step, the lenses 10, with the haptics attached,are extracted, or rinsed in distilled, purified water to remove anyresidues from the adhesive or impurities which may be present on thelens. The intraocular lenses are further agitated in the purified waterfor a period of at least 12 hours to draw out such impurities. Thelenses are then dried, and the haptic attachment is tested fordurability on a gram scale.

It will be understood by those skilled in the art that the coiningmandrel of the present invention can assume any desired configuration,and that the mold forming process described herein may be used forintraocular lenses other than biconvex. The foregoing detaileddescription is to be clearly understood as given by way of illustration,the spirit and scope of this invention limited solely by the appendedclaims.

What is claimed is:
 1. A method of making optical molds having anoptical power surface within the mold cavity, comprising the stepsof:forming a reverse mold configuration on a surface of a firstmaterial; treating said first material to form a hardened coiningmandrel; polishing said surface of said coining mandrel to produce anoptical finish; and pressing said coining mandrel into a blank formed ofa second material which is softer than said coining mandrel.
 2. A methodof making optical molds, as defined by claim 1, wherein said formingstep produces a coining mandrel which exhibits a shorter radius ofcurvature than the desired mold cavity to allow for "spring back" of thecoined optical surface.
 3. A method of making optical molds, as definedby claim 1, wherein said forming step produces a coining mandrel whichhas a larger surface area than that of the desired mold cavity to allowfor lens shrinkage, while said lens is being formed.
 4. A method ofmaking optical molds, as defined by claim 1, wherein said first materialis tool steel.
 5. A method of making optical molds, as defined by claim1, wherein said second material is stainless steel.
 6. A method ofmaking optical molds, as defined by claim 1, wherein said secondmaterial is sheet metal, having a resilient backing placed thereunder.7. A method of making optical molds, as defined by claim 1, wherein saidblank has an optically polished surface.
 8. A method of making opticalmolds, as defined by claim 4, wherein said steel is heat treated.
 9. Amethod of making optical molds, as defined by claim 8, wherein said heattreatment step comprises:evacuating air from an oven to produce a vacuumenvironment; heating said steel to at least 1,300°; and allowing saidsteel to slowly cool within said oven upon the cessation of said heatingstep.
 10. A method of making optical molds, as defined by claim 8,wherein said steel is heat treated in a nitrogen oven.
 11. A method ofmaking optical molds, as defined by claim 6, wherein said coiningmandrel is hardened to at least 40 Rockwell, Scale C.
 12. A method ofmaking optical molds, as defined by claim 5, wherein said coiningmandrel is hardened to at least 58 Rockwell, Scale C.
 13. A method ofmaking optical molds, as defined by claim 1, wherein said coiningmandrel is hardened to at least 60 Rockwell, Scale C.
 14. A method ofmaking optical molds, as defined by claim 1, wherein said surface ofsaid coining mandrel is peripherally radiused such that lenses producedin the resultant mold cavity will exhibit a single flash line.
 15. Amethod of making optical molds, as defined by claim 1, wherein saidpolishing step comprises:hand polishing said coining mandrel under amicroscope with a silicone carbide material; further optically polishingsaid surface of said coining mandrel with a mixture of aluminum oxideand machine oil; and tumbling said coining mandrel in a tumbler toenhance the optical finish.
 16. A method of making optical molds, asdefined by claim 15, wherein said tumbler contains machine oil, fumedsilicone dioxide, glass beads having a diameter of at least 1 mm andmineral spirits
 17. A method of making optical molds, as defined byclaim 1, wherein said coining mandrel is pressed into said blank using ahydraulic press.
 18. A method of making optical molds, as defined byclaim 17, wherein said hydraulic press is loaded to approximately 10tons.
 19. A method of making optical molds, as defined by claim 1,wherein said pressing step requires a pressure of at least 400,000p.s.i. to create a mold cavity of the desired depth.
 20. A method ofmaking optical molds, as defined by claim 14, wherein said blank ispermanently deformed during said pressing step so as to produce a moldhalf, having a mold cavity of optical quality.
 21. A method of makingoptical molds, as defined by claim 20, wherein the porosity of saidblank in the localized area of said mold cavity is decreased during saidpressing step.
 22. A method of making optical molds, as defined by claim20, wherein said mold half is work-hardened during said pressing step.23. A method of making optical molds, as defined by claim 20, wherein aridge of displaced material is formed around said mold cavity duringsaid pressing step.
 24. A method of making optical molds, as defined byclaim 20, wherein said mold cavity is ogive in shape.
 25. A method ofmaking optical molds, as defined by claim 20, further comprising thestep of grinding said ridge from said mold half to produce asubstantially flat surface surrounding said mold cavity.
 26. A method ofmaking optical molds, as defined by claim 25, further comprising thestep of machining an overflow groove into said flat surface of said moldhalf, proximate to and surrounding said mold cavity.
 27. A method ofmaking optical molds, as defined by claim 1, wherein said forming stepcomprises the steps of:machining an enlarged pattern surface,commensurate with said reverse mold configuration, scaled at apredefined ratio with respect to said coining mandrel; and replicatingsaid surface of said pattern onto said first material, scaled down tothe desired size.
 28. A method of making optical molds, as defined byclaim 27, wherein said forming step further comprises the stepsof:determining the amount of deformation said coining mandrel willundergo during said pressing step; and dimensionally correcting saidpattern to correct for said deformations.
 29. A method of making opticalmolds, as defined by claim 28, wherein said determining stepcomprises:determining the amount of axial compression said coiningmandrel will undergo during said pressing step; and determining theamount of radial expansion said coining mandrel will undergo during saidpressing step.
 30. A method of making optical molds, as defined by claim29, wherein said dimensional correcting step comprises:dimensioning saidpattern to allow for an axial compression of said coining mandrel on theorder of 0.012 inches.
 31. A method of making optical molds, as definedby claim 30, wherein said dimensional compressing step further comprisesthe step of:dimensioning said pattern to allow for a radial expansion ofsaid coining mandrel on the order of 0.001 inches.
 32. A method ofmaking optical molds, as defined by claim 1, wherein said pressing stepis performed by a hydraulic press which is loaded to approximately 7tons.
 33. A method of making optical molds, as defined by claim 1,wherein said coining mandrel contains a plurality of spherical sectors.34. A method of making optical molds, as defined by claim 1, whereinsaid coining mandrel contains a plurality of aspherical sectors.
 35. Amethod of making optical molds, as defined by claim 1, wherein saidcoining mandrel contains a plurality of aspherical and sphericalsectors.
 36. A method of making optical molds, as defined by claim 1,wherein said coining mandrel contains a plurality of symmetric sectors.37. A method of making optical molds, as defined by claim 1, whereinsaid coining mandrel contains a plurality of non-symmetric sectors. 38.A method of making optical molds, as defined by claim 1, wherein saidcoining mandrel has a higher modulus of elasticity than said blank. 39.A method of making optical molds, as defined by claim 1, wherein saidforming step comprises using an enlarged pattern to create said reversemold configuration.